Inter-layer reference picture construction for spatial scalability with different aspect ratios

ABSTRACT

A method of coding video data includes upsampling at least a portion of a reference layer picture to an upsampled picture having an upsampled picture size. The upsampled picture size has a horizontal upsampled picture size and a vertical upsampled picture size. At least one of the horizontal or vertical upsampled picture sizes may be different than a horizontal picture size or vertical picture size, respectively, of an enhancement layer picture. In addition, position information associated with the upsampled picture may be signaled. An inter-layer reference picture may be generated based on the upsampled picture and the position information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. Provisional Patent ApplicationNo. 61/773,102 entitled “INTER-LAYER REFERENCE PICTURE CONSTRUCTION FORSPATIAL SCALABILITY WITH DIFFERENT ASPECT RATIOS” filed on Mar. 5, 2013,the disclosure of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

This disclosure generally relates to video coding and compression. Inparticular, this disclosure is related to High Efficiency Video Coding(HEVC) and its extensions, e.g., scalable video coding (SVC), multi-viewvideo and 3D coding (MVC, 3DV), etc. In some embodiments, the disclosurerelates to coding (e.g., encoding or decoding) pictures having differentpicture aspect ratios (PARs) in SVC. In other embodiments, thedisclosure relates to signaling regions in a reference layer and/orenhancement layer that relate to inter-layer prediction.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC) standard presentlyunder development, and extensions of such standards. The video devicesmay transmit, receive, encode, decode, and/or store digital videoinformation by implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs), and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which may be quantized. The quantizedtransform coefficients may be initially arranged in a two-dimensionalarray and scanned in order to produce a one-dimensional vector oftransform coefficients, and entropy coding may be applied to achieveeven more compression.

SUMMARY

In accordance with some embodiments, an apparatus configured to codevideo information includes a processor configured upsample at least aportion of a reference layer picture to an upsampled picture having anupsampled picture size, the upsampled picture size comprising ahorizontal upsampled picture size and a vertical upsampled picture size.The processor may further be configured to signal position informationassociated with the upsampled picture. For example, the processor mayfurther be configured to determine the position information associatedwith the upsampled picture based on position information associated withan enhancement layer picture. The position information associated withthe enhancement layer picture may comprise coordinates of theenhancement layer picture. The processor may further be configured togenerate an inter-layer reference picture based on the upsampled pictureand the position information.

In some embodiments, a size of the upsampled portion of the referencelayer picture equals a size of the reference layer picture. Theprocessor may further be configured to send or receive the signaledposition information.

In some embodiments, the upsampled picture size is smaller than or equalto a size of the enhancement layer picture. For example, at least one ofthe horizontal or vertical upsampled picture sizes may be smaller than ahorizontal picture size or vertical picture size, respectively, of theenhancement layer picture. The processor may further be configured todetermine a size difference between the upsampled picture size and asize of the enhancement layer picture and increase the upsampled picturesize based on the size difference. In some embodiments, the processormay further be configured to increase the upsampled picture size bypadding pixel values to the upsampled picture, and determine a paddedpixel value based on a value of a nearest boundary pixel in theupsampled picture.

In some embodiments, the upsampled picture size is larger than or equalto a size of the enhancement layer picture. For example, at least one ofthe horizontal or vertical upsampled picture sizes may be larger than ahorizontal picture size or vertical picture size, respectively, of theenhancement layer picture. The processor may further be configured todetermine a size difference between the upsampled picture size and asize of the enhancement layer picture and reduce the upsampled picturesize based on the size difference. For example, the processor may beconfigured to decrease the upsampled picture size by cropping pixelvalues from the upsampled picture.

In some embodiments, the processor is further configured to determine anupsampling ratio for horizontal or vertical directions based at least inpart on the signaled position information. In some embodiments, theapparatus comprises a video encoder. In other embodiments, the apparatuscomprises a video decoder.

In another embodiment, a method of coding video information includesupsampling at least a portion of a reference layer picture to anupsampled picture having an upsampled picture size, the upsampledpicture size comprising a horizontal upsampled picture size and avertical upsampled picture size; and signaling position informationassociated with the upsampled picture. The method may further includedetermining the position information associated with the upsampledpicture based on position information associated with an enhancementlayer picture. For example, the position information associated with theenhancement layer picture may comprise coordinates of the enhancementlayer picture. The method may further include generating an inter-layerreference picture based on the upsampled picture and the positioninformation.

In another embodiment, a video coding apparatus includes a means forupsampling a reference layer picture to an upsampled picture having anupsampled picture size, the upsampled picture size comprising ahorizontal upsampled picture size and a vertical upsampled picture size;and a means for signaling position information associated with theupsampled picture. The video coding apparatus may further include ameans for determining the position information associated with theupsampled picture based on position information associated with anenhancement layer picture. The video coding apparatus may furtherinclude a determining a size difference between the upsampled picturesize and a size of an enhancement layer picture and increase theupsampled picture size based on the size difference.

In another embodiment, a non-transitory computer-readable medium havingstored thereon instructions that, when executed by a processor, causethe processor to upsample a reference layer picture to an upsampledpicture having an upsampled picture size, the upsampled picture sizecomprising a horizontal upsampled picture size and a vertical upsampledpicture size; and signal position information associated with theupsampled picture. The non-transitory computer-readable medium mayfurther have stored thereon instructions that when executed causes theprocessor to determine the position information associated with theupsampled picture based on position information associated with anenhancement layer picture. The non-transitory computer-readable mediummay further have stored thereon instructions that when executed causesthe processor to determine a size difference between the upsampledpicture size and a size of an enhancement layer picture and increase theupsampled picture size based on the size difference.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating scalabilities in three differentdimensions according to aspects of this disclosure.

FIG. 5 is a block diagram illustrating an example structure of ascalable video coding (SVC) bitstream according to aspects of thisdisclosure.

FIG. 6 is a block diagram illustrating example SVC access units in abitstream according to aspects of this disclosure.

FIG. 7 is a diagram illustrating an example of picture aspect ratioscalability between a reference layer and an enhancement layer.

FIG. 8 is a diagram illustrating another example of picture aspect ratioscalability between a reference layer and an enhancement layer.

FIG. 9 is a diagram illustrating an example of upsampling a portion of areference layer picture to an enhancement layer according to anembodiment.

FIG. 10A is a diagram illustrating an example of upsampling a referencelayer picture to an enhancement layer according to an embodiment.

FIG. 10B is a diagram illustrating an example of upsampling a referencelayer picture to an enhancement layer according to another embodiment.

FIG. 11A is a diagram illustrating an example of upsampling a referencelayer picture to an enhancement layer according to another embodiment.

FIG. 11B is a diagram illustrating an example of upsampling a referencelayer picture to an enhancement layer according to another embodiment.

FIG. 12 illustrates a method for coding video data according to anembodiment.

DETAILED DESCRIPTION

The techniques described in this disclosure are generally related toscalable video coding (SVC) and/or multiview/3D video coding. Forexample, the techniques may be related to, and used with or within aHigh Efficiency Video Coding (HEVC) scalable video coding (SVC)extension. In SVC, there can be multiple layers of video information. Alayer at the very bottom level or at the lowest level of the videoinformation may serve as a base layer (BL) or reference layer (RL), andthe layer at the very top level or at the highest level of the videoinformation may serve as an enhanced layer (EL). The “enhanced layer”may be considered as being synonymous with an “enhancement layer,” andthese terms may be used interchangeably. Layers between the BL and ELmay serve as ELs and/or RLs. For instance, a given layer may be an ELfor a layer below (e.g., that precedes) the given layer, such as thebase layer or any intervening enhancement layer. Further, the givenlayer may also serve as a reference layer for an enhancement layer above(e.g., subsequent to) the given layer. Any given layer in between thebase layer (e.g., the lowest layer having, for example, a layeridentification (ID) set or equal to “1”) and the top layer (or thehighest layer) may be used as a reference for inter-layer prediction bya layer higher relative to the given layer and may be determined using alayer lower to the given layer as a reference for inter-layerprediction.

For purposes of illustration only, the techniques described in thedisclosure are described with examples including only two layers (e.g.,a lower level layer such as the reference layer, and a higher levellayer such as the enhanced layer). It should be understood that theexamples described in this disclosure can be extended to examples withmultiple reference layers and enhancement layers as well. In addition,for ease of explanation, the following disclosure mainly uses the term“pictures.” However, these terms are not meant to be limiting. Forexample, the techniques described below can be used with other termsassociated with video units, such as blocks (e.g., CU, PU, TU,macroblocks, etc.), slices, frames, blocks, etc.

To support inter-layer prediction in SHVC, when an upsampled referencelayer picture is used as a reference picture in a reference picture listof an enhancement layer picture, a problem occurs when the resolution ofthe reference layer reconstructed picture, after upsampling, does notequal the resolution of the enhancement layer picture. For example, ingeneral, upsampling a reference layer picture increases the resolutionof the reference layer picture. In particular, upsampling a referencelayer picture increases a number of pixels in the upsampled referencelayer. Upsampling may be indicated by an upsampling scale factor S=N/M,where S indicates the upsampling scale factor, N indicates a number ofoutput pixels in the upsampled reference layer picture, and M indicatesa number of input pixels in the reference layer picture. The upsamplingscale factor may be the same in horizontal and vertical directions, orthe upsampling scale factor may be different. However, when an upsampledreference layer picture is used as a reference picture in a referencepicture list of an enhancement layer picture, a problem occurs becausethe upsampling scale factor may not be known. In addition, if theupsampled reference layer picture does not have the same resolution asthat of the enhancement layer picture, the upsampled reference layerpicture cannot be used directly (e.g., without further modification) asan inter-layer reference picture.

Another problem may occur with respect to signaling of the upsampledreference layer region with respect to the coordination of anenhancement layer picture. For example, if an enhancement layer pictureis predicted from multiple layers, signaling one set of parameterscorresponding to one layer may be insufficient. In addition, it ispossible that only part (e.g., a portion) of a reference layer picturemay be used for inter-layer prediction.

To reduce coding complexity and provide robust support for inter-layerprediction in SHVC, techniques may be used to provide for inter-layerreference picture construction from layers having different aspectratios. For example, in some embodiments, a method of coding video dataincludes upsampling at least a portion of a reference layer picture toan upsampled reference layer picture having an upsampled picture size.The upsampled picture size includes a horizontal upsampled picture sizeand a vertical upsampled picture size. Position information associatedwith the upsampled picture, such as an offset, may be signaled. Forexample, the position information associated with the upsampled picturemay be determined based on position information associated with anenhancement layer picture. In particular, the position of the upsampledenhancement layer may be specified by an offset relative to a boundaryof the enhancement layer picture. In addition, the position informationassociated with an enhancement layer picture based on may includecoordinates of the enhancement layer picture. For example, the offsetmay specify a number of pixels in the enhancement layer picture. Inaddition, an inter-layer reference picture may be generated based on theupsampled picture and the position information.

Video Coding Standards

Certain embodiments described herein relate to inter-layer predictionfor scalable video coding in the context of advanced video codecs, suchas HEVC (High Efficiency Video Coding). More specifically, the presentdisclosure relates to systems and methods for improved performance ofinter-layer prediction in scalable video coding (SVC) extension of HEVC.In the description below, H.264/AVC techniques related to certainembodiments are described; the HEVC standard and related techniques arealso discussed. While certain embodiments are described herein in thecontext of the HEVC and/or H.264 standards, one having ordinary skill inthe art may appreciate that systems and methods disclosed herein may beapplicable to any suitable video coding standard. For example,embodiments disclosed herein may be applicable to one or more of thefollowing standards: ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 orISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable VideoCoding (SVC) and Multiview Video Coding (MVC) extensions.

Scalable video coding (SVC) may be used to provide quality (alsoreferred to as signal-to-noise (SNR)) scalability, spatial scalabilityand/or temporal scalability. For example, in one embodiment, a referencelayer (e.g., a base layer) includes video information sufficient todisplay a video at a first quality level and the enhancement layerincludes additional video information relative to the reference layersuch that the reference layer and the enhancement layer together includevideo information sufficient to display the video at a second qualitylevel higher than the first level (e.g., less noise, greater resolution,better frame rate, etc.). An enhanced layer may have different spatialresolution than a reference layer. For example, the spatial aspect ratiobetween the upsampled picture and the reference layer picture can be1.0, 1.5, 2.0 or other different ratios. In other words, the spatialaspect of the upsampled picture may equal 1.0, 1.5, or 2.0 times thespatial aspect of the reference layer picture. In some examples, thescaling factor of the upsampled picture may be greater than thereference layer picture. For example, a size of pictures in theenhancement layer may be greater than a size of pictures in thereference layer. In this way, it may be possible, although not alimitation, that the spatial resolution of the enhancement layer islarger than the spatial resolution of the reference layer.

In the SVC extension for H.264, prediction of a current block may beperformed using the different layers that are provided for SVC. Suchprediction may be referred to as inter-layer prediction. Inter-layerprediction methods may be utilized in SVC in order to reduce inter-layerredundancy. Some examples of inter-layer prediction may includeinter-layer intra prediction, inter-layer motion prediction, inter-layermode prediction, and inter-layer residual prediction. Inter-layer intraprediction uses the reconstruction of collocated blocks in a referencelayer to predict the current block in the enhancement layer. Inter-layermotion prediction uses motion of the reference layer to predict motionin the enhancement layer. Inter-layer mode prediction predicts the modein the enhancement layer based on the mode in the reference layer.Inter-layer residual prediction uses the residue of the reference layerto predict the residue of the enhancement layer.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the invention. For example, an apparatus may be implemented or amethod may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure. As shown in FIG. 1, system 10 includes asource device 12 that provides encoded video data to be decoded at alater time by a destination device 14. In particular, source device 12provides the video data to destination device 14 via a computer-readablemedium 16. Source device 12 and destination device 14 may comprise anyof a wide range of devices, including desktop computers, notebook (e.g.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as so-called “smart” phones, so-called “smart” pads, televisions,cameras, display devices, digital media players, video gaming consoles,video streaming device, or the like. In addition, in some embodiments,system 10 can be implemented in a single device. For example, any suchsingle device, including a telephone handset, may comprise both sourcedevice 12 and destination device 14, as well as computer-readable medium16. In some cases, source device 12 and destination device 14 may beequipped for wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 1, source device 12 includes video source 18,video encoder 20, and output interface 22. In some embodiments, awireless communication device, such as a cellular telephone, cancomprise source device 12, including video source 18, video encoder 20,and output interface 22. Destination device 14 includes input interface28, video decoder 30, and display device 32. In some embodiments, awireless communication device, such as a cellular telephone, cancomprise destination device 14, including input interface 28, videodecoder 30, and display device 32. For example, in some cases, a singlewireless communication device can comprise both source device 12 anddestination device 14. In accordance with this disclosure, video encoder20 of source device 12 may be configured to apply the techniques forcoding a bitstream including video data conforming to multiple standardsor standard extensions. In other examples, a source device and adestination device may include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource 18, such as an external camera. Likewise, destination device 14may interface with an external display device, rather than including anintegrated display device.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor determining candidates for a candidate list for motion vectorpredictors for a current block may be performed by any digital videoencoding and/or decoding device. Although generally the techniques ofthis disclosure are performed by a video encoding device, the techniquesmay also be performed by a video encoder/decoder, typically referred toas a “CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device 12 and destinationdevice 14 are merely examples of such coding devices in which sourcedevice 12 generates coded video data for transmission to destinationdevice 14. In some examples, devices 12, 14 may operate in asubstantially symmetrical manner such that each of devices 12, 14include video encoding and decoding components. Hence, system 10 maysupport one-way or two-way video transmission between video devices 12,14, e.g., for video streaming, video playback, video broadcasting, orvideo telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. For example, in some embodiments in whichsource device 12 and destination device 14 are implemented as a singledevice, such as a wireless handset, computer-readable medium 16 caninclude any storage media. In some examples, a network server (notshown) may receive encoded video data from source device 12 and providethe encoded video data to destination device 14, e.g., via networktransmission, direct wired communication, etc. Similarly, a computingdevice of a medium production facility, such as a disc stampingfacility, may receive encoded video data from source device 12 andproduce a disc containing the encoded video data. Therefore,computer-readable medium 16 may be understood to include one or morecomputer-readable media of various forms, in various examples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., GOPs. Display device 32 displays the decoded video data toa user, and may comprise any of a variety of display devices such as acathode ray tube (CRT), a liquid crystal display (LCD), a plasmadisplay, an organic light emitting diode (OLED) display, or another typeof display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard, including but not limited to any of thestandards listed above. Other examples of video coding standards includeMPEG-2 and ITU-T H.263. In some aspects, video encoder 20 and videodecoder 30 may each be integrated with an audio encoder and decoder, andmay include appropriate MUX-DEMUX units, or other hardware and software,to handle encoding of both audio and video in a common data stream orseparate data streams. If applicable, MUX-DEMUX units may conform to theITU H.223 multiplexer protocol, or other protocols such as the userdatagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice. A device including video encoder 20 and/or video decoder 30 maycomprise an integrated circuit, a microprocessor, and/or a wirelesscommunication device, such as a cellular telephone.

The JCT-VC is working on development of the HEVC standard. The HEVCstandardization efforts are based on an evolving model of a video codingdevice referred to as the HEVC Test Model (HM). The HM presumes severaladditional capabilities of video coding devices relative to existingdevices according to, e.g., ITU-T H.264/AVC. For example, whereas H.264provides nine intra-prediction encoding modes, the HM may provide asmany as thirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. Syntax datawithin a bitstream may define a size for the LCU, which is a largestcoding unit in terms of the number of pixels. A slice includes a numberof consecutive treeblocks in coding order. A video frame or picture maybe partitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, the CU is referred as a leaf-CU. In this disclosure, foursub-CUs of a leaf-CU will also be referred to as leaf-CUs even if thereis no explicit splitting of the original leaf-CU. For example, if a CUat 16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, the TU may be referredto as a leaf-TU. Generally, for intra coding, all the leaf-TUs belongingto a leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up,” “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks may not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs including the residual data for the CU, and thentransform the TUs to produce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization is a broad term intended to have its broadest ordinarymeaning. In one embodiment, quantization refers to a process in whichtransform coefficients are quantized to possibly reduce the amount ofdata used to represent the coefficients, providing further compression.The quantization process may reduce the bit depth associated with someor all of the coefficients. For example, an n-bit value may be roundeddown to an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

Video encoder 20 may further send syntax data, such as block-basedsyntax data, frame-based syntax data, and GOP-based syntax data, tovideo decoder 30, e.g., in a frame header, a block header, a sliceheader, or a GOP header. The GOP syntax data may describe a number offrames in the respective GOP, and the frame syntax data may indicate anencoding/prediction mode used to encode the corresponding frame.

FIG. 2 is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to perform any orall of the techniques of this disclosure. As one example, mode selectunit 40 may be configured to perform any or all of the techniquesdescribed in this disclosure. However, aspects of this disclosure arenot so limited. In some examples, the techniques described in thisdisclosure, including the methods described below with respect to FIGS.9-12, may be shared among the various components of video encoder 20. Insome examples, in addition to or instead of, a processor (not shown) maybe configured to perform any or all of the techniques described in thisdisclosure.

Video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra-coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-prediction (B mode), may refer to any of severaltemporal-based coding modes.

As shown in FIG. 2, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 1, videoencoder 20 includes mode select unit 40, reference frame memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, and partition unit 48. For video block reconstruction, video encoder20 also includes inverse quantization unit 58, inverse transform unit60, and summer 62. A deblocking filter (not shown in FIG. 2) may also beincluded to filter block boundaries to remove blockiness artifacts fromreconstructed video. If desired, the deblocking filter would typicallyfilter the output of summer 62. Additional filters (in loop or postloop) may also be used in addition to the deblocking filter. Suchfilters are not shown for brevity, but if desired, may filter the outputof summer 50 (as an in-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference frame memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference frame memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra-prediction unit 46 may intra-predict or calculate a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra-prediction unit 46 may determine an intra-predictionmode to use to encode a current block. In some examples,intra-prediction unit 46 may encode a current block using variousintra-prediction modes, e.g., during separate encoding passes, andintra-prediction unit 46 (or mode select unit 40, in some examples) mayselect an appropriate intra-prediction mode to use from the testedmodes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bit rate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. Video encoder 20 may include in the transmittedbitstream configuration data, which may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used. In any case, transformprocessing unit 52 applies the transform to the residual block,producing a block of residual transform coefficients. The transform mayconvert the residual information from a pixel value domain to atransform domain, such as a frequency domain. Transform processing unit52 may send the resulting transform coefficients to quantization unit54. Quantization unit 54 quantizes the transform coefficients to furtherreduce bit rate. The quantization process may reduce the bit depthassociated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy codes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain, e.g., for later use as areference block. Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference frame memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in reference framememory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

FIG. 3 is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. Video decoder 30 may be configured to perform any orall of the techniques of this disclosure, including the methodsdescribed below with respect to FIGS. 9-12. As one example, motioncompensation unit 72 and/or intra prediction unit 74 may be configuredto perform any or all of the techniques described in this disclosure.However, aspects of this disclosure are not so limited. In someexamples, the techniques described in this disclosure may be sharedamong the various components of video decoder 30. In some examples, inaddition to or instead of, a processor (not shown) may be configured toperform any or all of the techniques described in this disclosure.

In the example of FIG. 3, video decoder 30 includes an entropy decodingunit 70, motion compensation unit 72, intra prediction unit 74, inversequantization unit 76, inverse transformation unit 78, reference framememory 82 and summer 80. Video decoder 30 may, in some examples, performa decoding pass generally reciprocal to the encoding pass described withrespect to video encoder 20 (FIG. 2). Motion compensation unit 72 maygenerate prediction data based on motion vectors received from entropydecoding unit 70, while intra-prediction unit 74 may generate predictiondata based on intra-prediction mode indicators received from entropydecoding unit 70.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors to and other syntax elements to motion compensationunit 72. Video decoder 30 may receive the syntax elements at the videoslice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (e.g., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference frame memory 92. Motioncompensation unit 72 determines prediction information for a video blockof the current video slice by parsing the motion vectors and othersyntax elements, and uses the prediction information to produce thepredictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit 76 inverse quantizes, e.g., de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter QP_(Y) calculated by videodecoder 30 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse integer transform, or a conceptually similar inversetransform process, to the transform coefficients in order to produceresidual blocks in the pixel domain.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 90represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference picture memory 92, which stores reference picturesused for subsequent motion compensation. Reference frame memory 82 alsostores decoded video for later presentation on a display device, such asdisplay device 32 of FIG. 1.

Motion Compensation in HEVC

As mentioned above, HEVC is the next generation of video codingstandard. In general, HEVC follows the framework of previous videocoding standards. The motion compensation loop of HEVC can be kept thesame as that in H.264/AVC, e.g., the reconstruction of the current frameÎ equals de-quantized coefficients r plus temporal prediction P:Î=r+P  (1)

-   -   where P indicates uni-directional prediction for P frames or        slices or bi-directional prediction for B frames or slices.

The unit of motion compensation in HEVC can be different from that inprevious video coding standards. In fact, the concept of macroblock inprevious video coding standards does not exist in HEVC. Instead, themacroblock concept is replaced by a highly flexible hierarchicalstructure based on a generic quadtree scheme. Within this scheme, threetypes of blocks, e.g., Coding Unit (CU), Prediction Unit (PU), andTransform Unit (TU), are defined. CU is the basic unit of regionsplitting. CU is analogous to the concept of macroblock, but CU does notrestrict the maximum size and CU allows recursive splitting into fourequal size CUs to improve the content adaptivity. PU is the basic unitof inter/intra prediction and PU may contain multiple arbitrary shapepartitions in a single PU to effectively code irregular image patterns.TU is the basic unit of transform. TU can be defined independently fromthe PU; however, TU's size is limited to the CU which the TU belongs to.This separation of the block structure into three different conceptsallows each to be optimized according to its role, which results in theimproved coding efficiency.

Scalable Video Coding

An example of scalabilities 400 in different dimensions is shown in FIG.4. In the example, scalabilities are enabled in three dimensions 402,404, 406. In a time dimension 402, frame rates, for example, with 7.5Hz, 15 Hz or 30 Hz can be supported by temporal scalability (T). Whenspatial scalability (S) 404 is supported, different resolutions, forexample, such as QCIF, CIF and 4CIF are enabled. For each specificspatial resolution and frame rate, the SNR (Q) layers 406 can be addedto improve the picture quality. Bitstreams from each layer 402, 404, 406can be multiplexed together into a single bitstream. Once video contenthas been encoded in such a scalable way, an extractor tool may be usedto adapt the actual delivered content according to applicationrequirements, which are dependent e.g., on the clients or thetransmission channel. In the example shown in FIG. 4, each cubic 408contains the pictures with the same frame rate (temporal level), spatialresolution and SNR layers. Better representation can be achieved byadding those cubes 408 (pictures) in any dimension 402, 404, 406.Combined scalability is supported when there are two, three or even morescalabilities enabled.

According to the SVC specification, the pictures with the lowest spatiallayer 410 and the lowest quality layer 412 are compatible withH.264/AVC, and the pictures at the lowest temporal level 414 form thetemporal base layer, which can be enhanced with pictures at highertemporal levels. In addition to the H.264/AVC compatible layer, severalspatial and/or SNR enhancement layers can be added to provide spatialand/or quality scalabilities. SNR scalability 406 is also referred asquality scalability. Each spatial enhancement layer 404 or SNRenhancement layer 406 itself may be temporally scalable, with the sametemporal scalability structure as the H.264/AVC compatible layer. Forone spatial or SNR enhancement layer, the lower layer the spatial or SNRenhancement layer depends on is also referred as the reference layer(e.g., base layer) of that specific spatial or SNR enhancement layer.

An example of SVC coding structure 500 is shown in FIG. 5. The pictureswith the lowest spatial and quality layer (pictures in layer 0 502 andlayer 1 504, with QCIF resolution) are compatible with H.264/AVC. Amongthem, those pictures of the lowest temporal level form the temporal baselayer, as shown in layer 0 502 of FIG. 5. This temporal base layer(layer 0) 502 can be enhanced with pictures of higher temporal levels(layer 1) 504. In addition to the H.264/AVC compatible layer 504,several spatial and/or SNR enhancement layers 506, 508, 510 can be addedto provide spatial and/or quality scalabilities. For instance, theenhancement layer can be a CIF representation with the same resolutionas layer 2 506. In the example, layer 3 508 is a SNR enhancement layer.As shown in the example, each spatial or SNR enhancement layer itselfmay be temporally scalable, with the same temporal scalability structureas the H.264/AVC compatible layer. Also, an enhancement layer canenhance both spatial resolution and frame rate. For example, layer 4 510provides a 4CIF enhancement layer, which further increases the framerate from 15 Hz to 30 Hz.

As shown in FIG. 6, the coded slices in the same time instance aresuccessive in the bitstream order and form one access unit 600 in thecontext of SVC. Those SVC access units 600 then follow the decodingorder, which could be different from the display order and is decidedby, for example, the temporal prediction relationship.

FIG. 7 illustrates a conceptual diagram of an example of picture aspectratio scalability between a reference layer and an enhancement layer. Insome embodiments, Picture Aspect Ratio (PAR) is the width:height ratioof a captured picture, where width and height are measured in the samelength (spatial measurement) units. Picture aspect ratio may beexpressed as X:Y, where X is horizontal width and Y is vertical height(in arbitrary units of spatial distance). In some embodiments, PictureSample Aspect Ratio (PSAR) is the ratio between the horizontal distancebetween the columns and the vertical distance between the rows of theluma sample array in a picture. Picture sample aspect ratio may beexpressed as h:v, where h is horizontal width and v is vertical height(in arbitrary units of spatial distance). FIG. 7 illustrates an examplein which PSAR is the same between a reference layer and an enhancementlayer, and the reference layer is a cropped version of the enhancementlayer. In particular, as shown, a reference layer 710 can comprise ahorizontal width 712 and a vertical height 714. For example, thehorizontal width 712 may be 853 pixels and the vertical height 714 maybe 480 pixels. An enhancement layer 720 can comprise a horizontal width722 and a vertical height 724. For example, the horizontal width 722 maybe 1280 pixels and the vertical height 724 may be 720 pixels. In thisfigure, the spatial resolution of the enhancement layer 720 is 1280×720,and the spatial resolution of the reference layer 710 is 853×480 (WVGA).Both the reference layer 710 and enhancement layer 720 have PSAR of 1.In this example, both the reference layer 710 and enhancement layer 720have a PAR of 16:9.

FIG. 8 illustrates a conceptual diagram of another example of pictureaspect ratio scalability between a reference layer and an enhancementlayer. FIG. 8 illustrates an example in which PSAR is the same between areference layer and an enhancement layer, and the reference layer is ascaled and cropped version of the enhancement layer. In particular, asshown, a reference layer 810 can comprise a horizontal width 812 and avertical height 814. For example, the horizontal width 812 may be 640pixels and the vertical height 814 may be 480 pixels. An enhancementlayer 820 can comprise a horizontal width 822 and a vertical height 824.For example, the horizontal width 822 may be 1280 pixels and thevertical height 824 may be 720 pixels. The reference layer 810 may bescaled, and it is possible part of the scaled region is used for topredict the enhancement layer 820. In FIG. 8, the spatial resolution ofthe enhancement layer is 1280×720 (PAR 16:9) and of the reference layeris 640×480 (PAR 4:3), and both the layers have PSAR of 1. So, theenhancement layer 820 has a different picture aspect ratio than thereference layer 810.

In SVC, the regions of the upsampled reference layer picture that may beused for inter-layer prediction may be defined in the sequence parameterset. Such a region may be referred to as the upsampled region. Theupsampled region may be smaller or larger than the current picture(e.g., an enhancement layer picture) in either vertical or horizontaldimensions. Table 1 illustrates an example of a sequence parameter setsvc extension.

TABLE 1 C Descriptor seq_parameter_set_svc_extension( ) { ...seq_scaled_ref_layer_left_offset 0 se(v) seq_scaled_ref_layer_top_offset0 se(v) seq_scaled_ref_layer_right_offset 0 se(v)seq_scaled_ref_layer_bottom_offset 0 se(v) } ... }

In addition, similar information may be present in a slice header. Ifexplicitly signaled, this information will overwrite the informationsignaled in sequence parameter set. Table 2 illustrates a slice headerin scalable extension.

TABLE 2 C Descriptor slice_header_in_scalable_extension( ) { ...scaled_ref_layer_left_offset 2 se(v) scaled_ref_layer_top_offset 2 se(v)scaled_ref_layer_right_offset 2 se(v) scaled_ref_layer_bottom_offset 2se(v) } ... } }

To support inter-layer prediction in SHVC when an upsampled referencelayer picture is utilized as a reference picture in a reference picturelist of the enhancement layer picture, difficulties may arise. Forexample, the reference layer reconstructed picture, after upsampling,may not have the same resolution as that of the enhancement layerpicture. Thus, the upsampled reference layer picture cannot be directlyused as an inter-layer reference picture.

In addition, when signaling the reference layer upsampled region withrespect to the coordination of an enhancement layer picture, additionaldifficulties may arise. For example, an enhancement layer picture mightbe predicted from multiple layers, thus signaling one set of parametercorresponding to one layer could be insufficient. Furthermore, it mightbe possible that only part of a reference layer picture might be usedfor inter-layer prediction.

To reduce coding complexity and provide robust support for inter-layerprediction in SHVC, techniques may be used to provide for inter-layerreference picture construction for layers with different aspect ratios.For example, in some embodiments, a method of coding video data includesupsampling at least a portion of a reference layer picture to anupsampled picture having an upsampled picture size, the upsampledpicture size comprising a horizontal upsampled picture size and avertical upsampled picture size, and signaling position informationassociated with the upsampled picture. The method may further includedetermining the position information associated with the upsampledpicture based on position information associated with an enhancementlayer picture. For example, the position information associated with theenhancement layer picture may include coordinates of the enhancementlayer picture, such as an offset relative to a boundary of theenhancement layer picture. If no position information is signaled, adefault value, such as zero, may be assumed. In some embodiments, a sizeof the upsampled portion of the reference layer picture equals a size ofthe reference layer picture. In addition, in some embodiments, at leastone of the horizontal or vertical upsampled picture sizes may match(e.g., equal) a horizontal picture size or a vertical picture size,respectively, of an enhancement layer picture. An inter-layer referencepicture may be generated based on the upsampled picture and the positioninformation.

For example, in some embodiments, only a selective part of a referencelayer picture is used to generate an inter-layer reference picture,based on a signaled relevant window for the current layer for thatspecific reference layer. The selective part of the reference layerpicture within the relevant region may be upsampled to a picture with asize equal to the upsampled region, after upsampling, the size of theupsampled region is always smaller than or equal to the picture size theenhancement layer picture. The upsampled region may be further signaledand is defined using the coordinates of the enhancement layer picture.

In other embodiments, the whole reference layer picture is upsampled.The upsampled region may be larger than the enhancement layer picture ineither vertical or horizontal dimension. As such, the upsampled regionmay need to be cropped (e.g., reduced in area size). When the upsampledregion is smaller than the enhancement layer picture in either verticalor horizontal dimension, the upsampled region may need to be padded. Theupsampled region may be further signaled and may be defined using thecoordinates of the enhancement layer picture.

In each of these embodiments, the signaled relevant window or the wholepicture size of the reference layer as well as the upsampled region maybe used to derive the upsampling ratio for horizontal or verticaldirection. In addition, based on the information of the upsampledregion, pixel values may be padded (e.g., added) around the alignedupsampled region of the reference layer picture to enlarge the upsampledpicture to be the same size as the current picture (e.g., theenhancement layer picture). For example, the padding can be done in away that pixels with value equal to 128 (or 2<<N, wherein N+1 is the bitdepth). In addition, padding can performed such that the left paddingregion is padded horizontally from the pixel value in the boundary pixelof the aligned upsampled region, the right padding region is paddedhorizontally from the pixel value in the boundary pixel of the alignedupsampled region; the top padding region is padded vertically from thepixel value in the boundary pixel of the aligned upsampled region; thebottom padding region is padded vertically from the pixel value in theboundary pixel of the aligned upsampled region; the top-left, top-right,bottom-left and bottom-right padding region, if available, is paddedhorizontally and after other regions are padded.

FIG. 9 is a diagram illustrating an example of upsampling a portion of areference layer picture to an enhancement layer according to anembodiment. In particular, as shown, a reference layer 910 can comprisea sub-portion 912. The sub-portion 912 may be specified based on areference layer left offset 914 a, reference layer right offset 914 b,reference layer bottom offset 914 c, and reference layer top offset 914d. For example, the reference layer left offset 914 a may specify adistance (e.g., an offset) between a left boundary of the referencelayer 910 and a left boundary of the sub-portion 912. The referencelayer right offset 914 b may specify a distance between a right boundaryof the reference layer 910 and a right boundary of the sub-portion 912.The reference layer bottom offset 914 c may specify a distance between abottom boundary of the reference layer 910 and a bottom boundary of thesub-portion 912. The reference layer top offset 914 d may specify adistance between a top boundary of the reference layer 910 and a topboundary of the sub-portion 912.

The sub-portion 912 of the reference layer 910 may be upsampled to anupsampled picture 922 that is a sub-portion of an enhancement layer 920.In this example, the size of the upsampled picture 922 includes ahorizontal upsampled picture size and a vertical upsampled picture size,but the horizontal or vertical upsampled picture sizes are less than ahorizontal picture size and a vertical picture size, respectively, ofthe enhancement layer 920.

The upsampled picture 922 may be specified based on an enhancement layerleft offset 924 a, enhancement layer right offset 924 b, enhancementlayer bottom offset 924 c, and enhancement layer top offset 924 d. Forexample, the enhancement layer left offset 924 a may specify a distance(e.g., an offset) between a left boundary of the enhancement layer 920and a left boundary of the sub-portion 922. The enhancement layer rightoffset 924 b may specify a distance between a right boundary of theenhancement layer 920 and a right boundary of the sub-portion 922. Theenhancement layer bottom offset 924 c may specify a distance between abottom boundary of the enhancement layer 920 and a bottom boundary ofthe sub-portion 922. The enhancement layer top offset 924 d may specifya distance between a top boundary of the enhancement layer 920 and a topboundary of the sub-portion 922.

FIGS. 10A and 10B are diagrams illustrating an example of upsampling areference layer picture to an enhancement layer wherein at least one ofthe horizontal or vertical upsampled picture sizes is smaller than ahorizontal picture size or vertical picture size, respectively, of theenhancement layer picture. In particular, in the example shown in FIG.10A, a horizontal upsampled picture size is smaller than the horizontalpicture size of the enhancement layer picture. For example, a referencelayer 1010 may be upsampled to an upsampled picture 1022 that is asub-portion of an enhancement layer 1020. The size of the upsampledpicture 1022 includes a horizontal upsampled picture size and a verticalupsampled picture size. The vertical upsampled picture size of theupsampled picture 1022 matches (e.g., equals) the vertical picture sizeof the enhancement layer 1020, but the horizontal picture size of theupsampled picture 1022 is smaller than the horizontal picture size ofthe enhancement layer 1020. To specify the position of the upsampledpicture 1022, position information associated with the upsampled picture1022 relative to the enhancement layer 1020 may be signaled. Forexample, the upsampled picture 1022 may be specified based on anenhancement layer left offset 1024 a and the enhancement layer rightoffset 1024 b. For example, the enhancement layer left offset 1024 a mayspecify a distance (e.g., an offset) between a left boundary of theenhancement layer 1020 and a left boundary of the upsampled picture1022. The enhancement layer right offset 1024 b may specify a distancebetween a right boundary of the enhancement layer 1020 and a rightboundary of the upsampled picture 1022. The enhancement layer leftoffset 1024 a and the enhancement layer right offset 1024 b may bespecified based on the coordinates of the enhancement layer picture1020.

In the example shown in FIG. 10B, both of a horizontal upsampled picturesize and vertical upsampled picture size are smaller than the horizontalpicture size and vertical picture size, respectively, of the enhancementlayer. For example, the reference layer 1010 may be upsampled to anupsampled picture 1022 that is a sub-portion of an enhancement layer1020. The vertical upsampled picture size of the upsampled picture 1022is smaller than the vertical picture size of the enhancement layer 1020,and the horizontal picture size of the upsampled picture 1022 is smallerthan the horizontal picture size of the enhancement layer 1020. Tospecify the position of the upsampled picture 1022, position informationmay be signaled. For example, the upsampled picture 1022 may bespecified based on an enhancement layer left offset 1024 a, theenhancement layer right offset 1024 b, the enhancement layer bottomoffset 1024 c, and the enhancement layer top offset 1024 d. For example,the enhancement layer left offset 1024 a may specify a distance betweena left boundary of the enhancement layer 1020 and a left boundary of theupsampled picture 1022. The enhancement layer right offset 1024 b mayspecify a distance between a right boundary of the enhancement layer1020 and a right boundary of the upsampled picture 1022. The enhancementlayer bottom offset 1024 c may specify a distance between a bottomboundary of the enhancement layer 1020 and a bottom boundary of theupsampled picture 1022. The enhancement layer top offset 1024 d mayspecify a distance between a top boundary of the enhancement layer 1020and a top boundary of the upsampled picture 1022. The enhancement layerleft offset 1024 a, the enhancement layer right offset 1024 b, theenhancement layer bottom offset 1024 c, and the enhancement layer topoffset 1024 d may be specified based on the coordinates of theenhancement layer picture 1020.

FIGS. 11A and 11B are diagrams illustrating an example of upsampling areference layer picture to an enhancement layer wherein at least one ofthe horizontal or vertical upsampled picture sizes is larger than ahorizontal picture size or vertical picture size, respectively, of theenhancement layer picture. In particular, in the example shown in FIG.11A, a vertical upsampled picture size is larger than the verticalpicture size of the enhancement layer. For example, a reference layer1110 may be upsampled to an upsampled picture 1122 that is a larger thanan enhancement layer 1120. In this example, the size of the upsampledpicture 1122 includes a horizontal upsampled picture size and a verticalupsampled picture size. The vertical upsampled picture size of theupsampled picture 1122 is larger than the vertical picture size of theenhancement layer 1120, but the horizontal picture size of the upsampledpicture 1122 matches the horizontal picture size of the enhancementlayer 1120. To specify the position of the upsampled picture 1122,position information may be signaled. For example, the upsampled picture1122 may be specified based on an enhancement layer bottom offset 1124 cand the enhancement layer top offset 1124 d. For example, theenhancement layer bottom offset 1124 c may specify a distance between abottom boundary of the enhancement layer 1120 and a bottom boundary ofthe upsampled picture 1122. The enhancement layer top offset 1124 d mayspecify a distance between a top boundary of the enhancement layer 1120and a top boundary of the upsampled picture 1122. The enhancement layerbottom offset 1124 c and the enhancement layer top offset 1124 d may bespecified based on the coordinates of the enhancement layer picture1120.

In the example shown in FIG. 11B, both of a horizontal upsampled picturesize and vertical upsampled picture size are larger than the horizontalpicture size and vertical picture size, respectively, of the enhancementlayer. For example, a reference layer 1110 may be upsampled to anupsampled picture 1122 that is a larger than an enhancement layer 1120.The vertical upsampled picture size of the upsampled picture 1122 islarger than the vertical picture size of the enhancement layer 1120, andthe horizontal picture size of the upsampled picture 1122 is larger thanthe horizontal picture size of the enhancement layer 1120. To specifythe position of the upsampled picture 1122, position information may besignaled. For example, the upsampled picture 1122 may be specified basedon an enhancement layer left offset 1124 a, the enhancement layer rightoffset 1124 b, the enhancement layer bottom offset 1124 c, and theenhancement layer top offset 1124 d. For example, the enhancement layerleft offset 1124 a may specify a distance between a left boundary of theenhancement layer 1120 and a left boundary of the upsampled picture1122. The enhancement layer right offset 1124 b may specify a distancebetween a right boundary of the enhancement layer 1120 and a rightboundary of the upsampled picture 1122. The enhancement layer bottomoffset 1124 c may specify a distance between a bottom boundary of theenhancement layer 1120 and a bottom boundary of the upsampled picture1122. The enhancement layer top offset 1124 d may specify a distancebetween a top boundary of the enhancement layer 1120 and a top boundaryof the upsampled picture 1122. The enhancement layer left offset 1124 a,the enhancement layer right offset 1124 b, the enhancement layer bottomoffset 1124 c, and the enhancement layer top offset 1124 d may bespecified based on the coordinates of the enhancement layer picture1120.

For purposes of illustration, the techniques described in the disclosureare described using examples where there are only two layers. One layercan include a lower level layer or reference layer, and another layercan include a higher level layer or enhancement layer. For example, thereference layer can include a base layer or a temporal reference on anenhancement layer, and the enhancement layer can include an enhancedlayer relative to the reference layer. It should be understood that theexamples described in this disclosure extend to multiple enhancementlayers as well.

In some embodiments, a relevant window in the base view is signaled,relative to the picture size of the reference layer and the boundary ofthe relevant window is aligned or positioned within the reference layerpicture. In addition, the upsampled region may also be signaled. Theboundary of the upsampled region may be within the enhancement layerpicture. When an inter-layer reference picture is to be added into areference picture list of the enhancement layer picture, the upsampledregion is extended (e.g., by padding) to be the same size as that of theenhancement layer picture.

Syntax elements may be signaled in the video parameter set.Alternatively, syntax elements can be transmitted by a first flag in thebitstream, e.g., in a VPS (video parameter set), SPS (sequence parameterset), PPS (picture parameter set), slice header, or an SEI (supplementalenhancement information) message.

The syntax elements scaled ref_layer_left_offset[i][j],scaled_ref_layer_top_offset[i][j], scaled_ref_layer_right_offset[i][j],scaled_ref_layer_bottom_offset[i][j] may be collectively referred to asoffset between the scaled (upsampled) region and the enhancement layerpicture. The values they represent may be referred to as scaledreference layer offsets, of the j-th reference layer of layer i.

The syntax elements rel_scaled_ref_layer_left_offset[i][j],rel_scaled_ref_layer_top_offset[i][j],rel_scaled_ref_layer_right_offset[i][j], andrel_scaled_ref_layer_bottom_offset[i][j] may be collectively referred toas offset syntax elements of the relevant region of the reference layer,and the values they indicate may be referred to as the relevant regionoffsets of the j-th reference layer of layer i. Table 3 illustrates anexample of Video Parameter Set Extension Syntax.

TABLE 3 Descriptor vps_extension( ) { ... for( i = 0; i <=vps_max_layers_minus1; i++ ) for( j = 0; j < num_direct_ref_layers[ i ];j++ ) { scaled_ref_layer_left_offset[ i ][ j ] ue(v)scaled_ref_layer_top_offset[ i ][ j ] ue(v)scaled_ref_layer_right_offset[ i ][ j ] ue(v)scaled_ref_layer_bottom_offset[ i ][ j ] ue(v)rel_ref_layer_left_offset[ i ][ j ] ue(v) rel_ref_layer_top_offset[ i ][j ] ue(v) rel_ref_layer_right_offset[ i ][ j ] ue(v)rel_ref_layer_bottom_offset[ i ][ j ] ue(v) } ... }

In addition, scaled_ref_layer_left_offset[i][j],scaled_ref_layer_top_offset[i][j], scaled_ref_layer_right_offset[i][j],scaled_ref_layer_bottom_offset[i][j] may specify the distance (e.g., inunits of two luma samples), of the left, top, right, and bottomboundaries of the scaled reference region from the j-th reference layerof layer i to the left, top, right and bottom boundaries, respectively,of a current picture (e.g., the enhancement layer picture) of layer ithat is being decoded. When not present, the values of these syntaxelements may be inferred to be equal to 0.

Also, rel_scaled_ref_layer_left_offset[i][j],rel_scaled_ref_layer_top_offset[i][j],rel_scaled_ref_layer_right_offset[i][j],rel_scaled_ref_layer_bottom_offset[i][j] may specify the distance (e.g.,in units of two luma samples), of the left, top, right, and bottomboundaries of the decoded reference layer picture from the j-threference layer of layer i with respect to the left, top, right andbottom boundaries, respectively, of the relevant region of the decodedreference layer picture that is to be scaled for inter-layer-predictionfor current picture (e.g., the enhancement layer picture) of layer i.When not present, the values of these syntax elements may be inferred tobe equal to 0.

Alternatively, the signaling of the offsets for each reference layer maybe conditioned on a flag that is signaled for each reference layer,described as follows. For example, Table 4 illustrates an example of vpsextensions.

TABLE 4 Descriptor vps_extension( ) { ... for( i = 0; i <=vps_max_layers_minus1; i++ ) for( j = 0; j < num_direct_ref_layers[ i ];j++ ) { signal_ref_layer_offsets_flag[ i ][ j ] u(1) if(signal_ref_layer_offsets_flag[ i ][ j ] ) {scaled_ref_layer_left_offset[ i ][ j ] ue(v)scaled_ref_layer_top_offset[ i ][ j ] ue(v)scaled_ref_layer_right_offset[ i ][ j ] ue(v)scaled_ref_layer_bottom_offset[ i ][ j ] ue(v)rel_ref_layer_left_offset[ i ][ j ] ue(v) rel_ref_layer_top_offset[ i ][j ] ue(v) rel_ref_layer_right_offset[ i ][ j ] ue(v)rel_ref_layer_bottom_offset[ i ][ j ] ue(v) } } ... }

In addition, signal_ref_layer_offsets_flag[i][j] equal to 1 means thatthe scaled reference layer offset syntax elements and the offset syntaxelements of the relevant region of reference layer are signaled for thej-th reference layer of layer i. signal_ref_layer_offsets_flag[i][j]equal to 0 means that the scaled reference layer offsets and the offsetsyntax elements are not signaled for the j-th reference layer of layer iand are all inferred to be equal to 0.

Alternatively, the number of reference layers for which the scaledreference layer offsets would be signaled for each layer i would besignaled and the layer ID of the reference layer would be signaled inaddition to identify the layer ID. Table 5 illustrates another exampleof vps extensions.

TABLE 5 Descriptor vps_extension( ) { ... for( i = 0; i <=vps_max_layers_minus1; i++ ) { num_ref_layers_with_offsets[ i ] ue(v)for(j = 0; j < num_ref_layers_with_offsets[ i ]; j++ ) { ref_layer_id[ i][ j ] u(v) scaled_ref_layer_left_offset[ i ][ j ] ue(v)scaled_ref_layer_top_offset[ i ][ j ] ue(v)scaled_ref_layer_right_offset[ i ][ j ] ue(v)scaled_ref_layer_bottom_offset[ i ][ j ] ue(v)rel_ref_layer_left_offset[ i ][ j ] ue(v) rel_ref_layer_top_offset[ i ][j ] ue(v) rel_ref_layer_right_offset[ i ][ j ] ue(v)rel_ref_layer_bottom_offset[ i ][ j ] ue(v) } } ... }

In addition, num_ref_layers_with_offsets[i] equals the number ofreference layers of layer i for which the scaled reference layer offsetsand the relevant region of the reference layer are signaled. The valueof num ref layers with offsets[i] will be in the range of 0 tonum_direct_ref_layers[i], inclusive.

ref_layer_id[i][j] equals the layer identifier of the reference layerfor which the scaled reference layer offsets and the relevant region ofthe reference layer are signaled in the loop. The number of bits used torepresent ref_layer_id[i][j] is Ceil(Log2(num_direct_ref_layers+1)).

To obtain the reference layer picture for the current layer, thederivation process is used once for luma samples with input Z equal to Land once for the chroma samples with input Z equal to C to obtain thevariables used in the process. The variables SubWidth_(L), andSubHeight_(L) may be both set equal to 1, and the variables SubWidth_(C)and SubHeight_(C) may be set equal to SubWidthC and SubHeightC,respectively.

In some embodiments, a variable Z, with possible values L or C, may beinput to this process. Let RefPicWidthInLumaSamples[i][j] andRefPicHeightInLumaSamples[i][j] be the width and height, respectively,of the j-th reference layer picture of the i-th layer in units of lumasamples as defined in the VPS, for i in the range of 0 tovps_max_layers_minus1, inclusive, and j in the range of 0 tonum_direct_ref_layers[i]−1, inclusive. Let CurrPicWidthInLumaSamples[i]and CurrPicHeightInLumaSamples[i] be the width and height, respectively,of the picture of the i-th layer, where i is in the range of 0 tovps_max_layers_minus1, inclusive. The picture widths and heights for thecurrent picture (e.g., the enhancement layer picture) and the referencepictures may be those defined by the syntax elementspic_width_in_luma_samples and pic_height_in_luma_samples for therespective pictures.

The relevant reference layer may be obtained using the relevantreference region offset syntax elements and the corresponding referencelayer width and heights. The variables RelRefLayerPicWidth_(Z)[i][j] andRelRefLayerPicHeight_(Z)[i][j] may be derived as follows:

RelRefLayerLeftOffset_(Z)[ i ][ j ] = rel_ref_layer_left_offset[ i ][ j] << (2 − SubWidth_(Z)) RelRefLayerTopOffset_(Z)[ i ][ j ] =rel_ref_layer_top_offset[ i ][ j ] << (2 − SubHeight_(Z))RelRefLayerRightOffset_(Z)[ i ][ j ] = rel_ref_layer_right_offset[ i ][j ] << (2 − SubWidth_(Z)) RelRefLayerBottomOffset_(Z)[ i ][ j ] =rel_ref_layer_bottom_offset[ i ][  j ] << (2 − SubHeight_(Z))RelRefLayerPicWidth_(Z)[ i ][ j ] = RefPicWidthInLumaSamples[ i ][ j] >> ( SubWidth_(Z) − 1 ) − RelRefLayerLeftOffset_(Z)[ i ][ j ] −RelRefLayerRightOffset_(Z)[ i ][ j ] RelRefLayerPicHeight_(Z)[ i ][ j ]= RefPicHeightInLumaSamples[ i ][ j ] >> ( SubHeight_(Z) − 1 ) −RelRefLayerTopOffset_(Z)[ i ][  j ] − RelRefLayerBottomOffset_(Z)[ i ][j ]

The scaled/upsampled region may be obtained by the variablesScaledRefLayerPicWidth_(Z)[i][j] and ScaledRefLayerPicHeight_(Z)[i][j],as derived below:

ScaledRefLayerLeftOffset_(Z)[ i ][ j ] = scaled_ref_layer_left_offset[ i][  j ] << (2 − SubWidth_(Z)) ScaledRefLayerTopOffset_(Z)[ i ][ j ] =scaled_ref_layer_top_offset[ i ][  j ] << (2 − SubHeight_(Z))ScaledRefLayerRightOffset_(Z)[ i ][ j ] = scaled_ref_layer_right_offset[ i ][ j ] << (2 − SubWidth_(Z)) ScaledRefLayerBottomOffset_(Z)[ i ][ j ]=  scaled_ref_layer_bottom_offset[ i ][ j ] << (2 − SubHeight_(Z))ScaledRefLayerPicWidth_(Z)[ i ][ j ] = CurrPicWidthInLumaSamples[ i ] >> ( SubWidth_(Z) − 1 )− ScaledRefLayerLeftOffset_(Z)[ i ][ j ] − ScaledRefLayerRightOffset_(Z)[ i ][ j ] ScaledRefLayerPicHeight_(Z)[ i][ j ] = CurrPicHeightInLumaSamples[  i ] >> ( SubHeight_(Z) − 1 )−ScaledRefLayerTopOffset_(Z)[ i ][ j ] −  ScaledRefLayerBottomOffset_(Z)[i ][ j ]

For ease of description of the following decoding process, the termsLeftStart_(Z)[i][j], TopStart_(Z)[i][j], RightEnd_(Z)[i][j] andBottomEnd_(Z)[i][j] may be defined as follows:

LeftStart_(Z)[ i ][ j ] = ScaledRefLayerLeftOffset_(Z)[ i ][ j ]TopStart_(Z)[ i ][ j ] = ScaledRefLayerTopOffset_(Z)[ i ][ j ]RightEnd_(Z)[ i ][ j ] = CurrPicWidthInLumaSamples[ i ] >> (SubWidth_(Z) − 1 )− ScaledRefLayerRightOffset_(Z)[ i ][ j ]BottomEnd_(Z)[ i ][ j ] = CurrPicHeightInLumaSamples[ i ] >> (SubHeight_(Z) − 1 )− ScaledRefLayerBottomOffsef_(Z)[ i ][ j ]

In some embodiments, the upsampling ratios may be calculated based onthe signaled relevant region in reference layer and the upsampledregion:scaleFactorX=(RightEnd_(Z) [i][j−LeftStart_(Z)[i][j])/(RelRefLayerPicWidth_(Z) [i][j]);scaleFactorY=(BottomEnd_(Z) [i][j]−TopStart_(Z)[i][j])/(RelRefLayerPicHeight_(Z) [i][j).

When upsampling the relevant region in the reference layer, the regionmay be padded for several pixels or extended in a way of using theexisting pixels in the reference picture. However, the calculation ofthe upsampling ratio for each dimension may be decided by the signaledrelevant region in the reference layer and the upsampled region in theenhancement layer. Any of a variety of upsampling methods, padding orextending methods can be used together with the techniques and methodsdescribed herein.

In some embodiments, the scaled reference layer may be padded beforebeing used as a reference picture for the layer i. The scaled and paddedpicture of the j-th reference layer of layer i, which may be used forinter-layer prediction for layer i, is denoted byScaledPaddedRefLayer_(A)[x][y], for A taking values L, Cb or Cr todenote luma samples, Cb samples and Cr samples, respectively. LetRefLayer_(A)[i][j] denote the reference layers samples of the j-threference layer of layer i corresponding to channel A (luma, Cb or Cr).The relevant region of the reference layer will occupy those samplesRefLayer_(A)[x][y] for x in the range of RelRefLayerLeftOffset_(Z)[i][j]toRefPicWidthInLumaSamples[i][j]>>(SubWidth_(Z)−1)−RelRefLayerRightOffset_(Z)[i][j]−1,inclusive, and y in the range of RelRefLayerTopOffset_(Z)[i][j] toRefPicHeightInLumaSamples[i][i]>>(SubHeight_(Z)−1)−RelRefLayerBottomOffset_(Z)[i][i]−1,inclusive. The upsampled picture occupies ScaledPaddedRefLayerA[m][n],for m in the range of LeftStart_(Z)[i][j] to RightEnd_(Z)[i][j]−1,inclusive, and n in the range of TopStart_(Z)[i][j] toBottomEnd_(Z)[i][j]−1, inclusive.

The final ScaledPaddedRefLayer_(A)[x][y] is obtained after the paddingoperation as described below with input A. After upsampling, the scaledreference layer is further padded in horizontal and/or verticaldirections to create an inter-layer reference picture having the sameresolution as the current picture (e.g., the enhancement layer picture).A variable A, with possible values L, Cb or Cr, is input to this method.When A equal to L, Z is set equal to L, and when A equal to Cb or Cr, Zis set equal to C. Table 6 illustrates example code that describes apadding operation.

TABLE 6   for( x = 0; x < LeftStart_(Z)[ i ][ j ]; x++ )     for( y =TopStart_(Z)[ i ][ j ]; y < BottomEnd_(Z)[ i ][ j ]; y++ )      ScaledPaddedRefLayerA[ x ][ y ] = ScaledPaddedRefLayer_(A)[LeftStart_(Z)[ i ][ j ] ][ y ]   for( x = RightEnd_(Z)[ i ][ j ]; x <CurrPicWidthInLumaSamples[ i ][ i ] >> (SubWidth_(Z) − 1); x++ )    for( y = TopStart_(Z)[ i ][ j ]; y < BottomEnd_(Z)[ i ][ j ]; y++ )      ScaledPaddedRefLayer_(A)[ x ][ y ] = ScaledPaddedRefLayer_(A)[RightEnd_(Z)[ i ][ j ] − 1 ][ y ]   for( x = 0; x <CurrPicWidthInLumaSamples[ i ][ i ] >>   (SubWidth_(Z) − 1); x++ )    for( y = 0; y < TopStart_(Z)[ i ][ j ]; y++ )      ScaledPaddedRefLayer_(A)[ x ][ y ] = ScaledPaddedRefLayer_(A)[ x][ TopStart_(Z)[ i ][ j ] ]   for( x = 0; x < CurrPicWidthInLumaSamples[i ][ i ] >>   (SubWidth_(Z) − 1); x++ )     for( y = BottomEnd_(Z)[ i ][j ]; y < CurrPicHeightInLumaSamples[ i ][ i ] >> (SubHeight_(Z) − 1);y++ )       ScaledPaddedRefLayer_(A)[ x ][ y ] =ScaledPaddedRefLayer_(A)[ x ][ BottomEnd_(Z)[ i ][ j ] − 1 ]

Alternately, the padding of the top and the bottom parts of the scaledreference layer picture can be done first followed by the padding of theleft and right parts of the scaled reference layer picture. Table 7provides an example of this padding approach.

TABLE 7   for( x = LeftStart_(Z)[ i ][ j ]; x <RightEnd_(Z)[ i ][ j ];x++ )     for( y = 0; y < TopStart_(Z)[ i ][ j ]; y++ )      ScaledPaddedRefLayer_(A)[ x ][ y ] = ScaledPaddedRefLayer_(A)[ x][ TopStart_(Z)[ i ][ j ] ]   for( x = LeftStart_(Z)[ i ][ j ]; x <RightEnd_(Z)[ i ][ j ]; x++ )     for( y = BottomEnd_(Z)[ i ][ j ]; y <CurrPicHeightInLumaSamples[ i ][ i ] >> (SubHeight_(Z) − 1); y++ )      ScaledPaddedRefLayer_(A)[ x ][ y ] = ScaledPaddedRefLayer_(A)[ x][ BottomEnd_(Z)[ i ][ j ] − 1]   for( x = 0; x < LeftStart_(Z)[ i ][ j]; x++ )     for( y = 0; y < CurrPicHeightInLumaSamples[ i ][ i ] >>(SubHeight_(Z) − 1); y++ )       ScaledPaddedRefLayer_(A)[ x ][ y ] =ScaledPaddedRefLayer_(A)[ LeftStart_(Z)[ i ][ j ] ][ y ]   for( x =RightEnd_(Z)[ i ][ j ]; x < CurrPicWidthInLumaSamples[ i ][ i ] >>(SubWidth_(Z) − 1); x++ )     for( y = 0; y <CurrPicHeightInLumaSamples[ i ][ i ] >> (SubHeight_(Z) − 1); y++ )      ScaledPaddedRefLayer_(A)[ x ][ y ] = ScaledPaddedRefLayer_(A)[RightEnd_(Z)[ i ][ j ] − 1 ][ y ]Alternatively, all the pixels in the ScaledPaddedRefLayerA[x][y] thatare not covered by the scaled reference layer picture may filled by aconstant value.

In some embodiments, the entire decoded reference layer picture isupsampled. When the value of any of the scaled reference layer offsetsis negative, cropping may be applied on the scaled reference layer suchthat the boundaries of the picture after cropping are within the decodedpicture boundaries of the current picture (e.g., the enhancement layerpicture). In this case, the upsampled region may be smaller or largerthan the enhancement layer picture.

Syntax elements may be signaled in a video parameter set. Alternatively,such syntax elements can be transmitted in sequence parameter set, orslice header extension, etc. Table 8 provides an example of VideoParameter Set Extension Syntax.

TABLE 8 Descriptor vps_extension( ) { ... for( i = 0; i <=vps_max_layers_minus1; i++ ) for( j = 0; j < num_direct_ref_layers[ i ];j++ ) { scaled_ref_layer_left_offset[ i ][ j ] se(v)scaled_ref_layer_top_offset[ i ][ j ] se(v)scaled_ref_layer_right_offset[ i ][ j ] se(v)scaled_ref_layer_bottom_offset[ i ][ j ] se(v) } ... }

In some embodiments, the syntax elementsscaled_ref_layer_left_offset[i][j], scaled_ref_layer_top_offset[i][j],scaled_ref_layer_right_offset[i][j],scaled_ref_layer_bottom_offset[i][j] specify the distance, in units oftwo luma samples, of the left, top, right, and bottom boundaries of thescaled decoded reference layer picture from the j-th reference layer oflayer i to the left, top, right and bottom boundaries, respectively, ofa current picture (e.g., the enhancement layer picture) of layer i thatis being decoded. When the scaled reference layer boundary is outsidethe enhancement layer picture, the distance is specified as a negativenumber. When not present, the values of these syntax elements areinferred to be equal to 0.

Alternatively, the signaling of the scaled reference layer offset syntaxelements may be condition based on a flag, which is also signaled foreach reference layer of layer i, similar to the techniques describedabove. Alternatively, the number of reference layers for layer i forwhich the scaled reference layer offset syntax elements would beexplicitly present is signaled, followed by list of the reference layerID and the corresponding scaled reference layer offset syntax elements,similar to the techniques described above.

The variables ScaledRefLayerLeftOffset_(Z)[i][j],ScaledRefLayerTopOffset_(Z)[i][j], ScaledRefLayerRightOffset_(Z)[i][j],ScaledRefLayerBottomOffset_(Z)[i][j], ScaledRefLayerPicWidth_(Z)[i][j]and ScaledRefLayerPicHeight_(Z)[i][j] may be derived in the same way asdiscussed above.

After upsampling the scaled reference layer is further padded or croppedin horizontal or vertical direction to create an inter-layer referencepicture having the same resolution as the current picture (e.g., theenhancement layer picture). The scaled reference layer is of sizeScaledRefLayerPicWidth_(Z)[i][j] samples in width andScaledRefLayerPicHeight_(Z)[i][j] samples in height. Let the scaledreference layer j of layer i be ScaledLayer_(A)[x][y] for x in the rangeof 0 to ScaledRefLayerPicWidth_(Z)[i][j]−1, inclusive and y in the rangeof 0 to ScaledRefLayerPicHeight_(Z)[i][j]−1, inclusive. This picture mayneed to be cropped to ensure that the scaled reference picture doesextend beyond the boundaries of the current picture (e.g., theenhancement layer picture) of layer i that is being decoded. Thevariables LeftStart_(Z)[i][j], TopStart_(Z)[i][j], RightEnd_(Z)[i][j]and BottomEnd_(Z)[i][j] may be derived as follows.

  LeftStart_(Z)[ i ][ j ] = Max( 0, ScaledRefLayerLeftOffset_(Z)[ i ][ j] )   TopStart_(Z)[ i ][ j ] = Max( 0, ScaledRefLayerTopOffset_(Z)[ i ][j ] )   RightEnd_(Z) [ i ][ j ] = Min( CurrPicWidthInLumaSamples[      i ] >> ( SubWidth_(Z) − 1 ),       CurrPicWidthInLumaSamples[ i] >> ( SubWidth_(Z) − 1 )− ScaledRefLayerRightOffset_(Z)[ i ][ j ] )  BottomEnd_(Z)[ i ][ j ] = Min( CurrPicHeightInLumaSamples[ i ][ >> (SubHeight_(Z) − 1 ),       CurrPicHeightInLumaSamples[ i ][ >> (SubHeight_(Z) − 1 )− ScaledRefLayerBottomOffsef_(Z)[ i ][ j ] )

The samples of the scaled reference layer picture that will be obtainedafter cropping is stored as ScaledPaddedRefLayer_(A)[x][y], and derivedas follows. In the following derivation, when A is equal to L (luma), Zequals L and when A is equal to Cb or Cr (chroma), Z equals C.

ScaledPaddedRefLayer_(A)[x][y] may be set equal toScaledLayer_(A)[x−ScaledRefLayerLeftOffset_(Z)[i][j]][y−ScaledRefLayerTopOffset_(Z)[i][j]], for x in the range of to LeftStart_(Z)[i][j] toRightEnd_(Z)[i][j]−1, inclusive and y in the range of TopStart_(Z)[i][j]to BottomEnd_(Z)[i][j]−1, inclusive. Padding may then be performed onthe ScaledPaddedRefLayer_(A)[x][y] as described above. In addition, anycombinations of the above embodiments may also be provided.

FIG. 12 illustrates an example method 1200 for coding video dataaccording to an example embodiment. The method 1200 can be performed byone or more components of video encoder 20 or video decoder 30, forexample. In some embodiments, other components may be used to implementone or more of the steps described herein.

At block 1202, at least a portion of a reference layer picture can beupsampled to an upsampled picture having an upsampled picture size. Insome embodiments, the reference layer picture can be obtained orreceived from video information from a memory. The upsampled picturesize can comprise a horizontal upsampled picture size and a verticalupsampled picture size. In some embodiments, at least one of thehorizontal or vertical upsampled picture sizes may be different than ahorizontal picture size or vertical picture size, respectively, of anenhancement layer picture. For example, at least one of the horizontalor vertical upsampled picture sizes may be smaller than a horizontalpicture size or vertical picture size, respectively, of the enhancementlayer picture. Alternatively, at least one of the horizontal or verticalupsampled picture sizes may be larger than a horizontal picture size orvertical picture size, respectively, of the enhancement layer picture.

At block 1204, position information associated with the upsampledpicture may be signaled. For example, the position informationassociated with the upsampled picture may be determined based onposition information associated with an enhancement layer picture. Insome embodiments, the position information associated with theenhancement layer picture includes coordinates of the enhancement layerpicture. An inter-layer reference picture may be generated based on theupsampled picture and the position information.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniques canbe fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. An apparatus configured to code videoinformation, comprising: a processor configured to: encode or decode aplurality of reference layer offset values each indicative of a distanceof a reference layer (RL) portion of a reference layer picture in areference layer from a corresponding edge of the reference layerpicture, the RL portion corresponding to a portion of the referencelayer picture that is to be used to predict at least part of anenhancement layer picture in an enhancement layer; determine the RLportion of the reference layer picture in the reference layer using theplurality of reference layer offset values, the RL portion being smallerthan the reference layer picture; encode or decode enhancement layeroffset values each indicative of a distance from corresponding edges ofthe enhancement layer picture to a first enhancement layer (EL) portionof the enhancement layer picture that is to be predicted based on thereference layer picture, the EL portion of the enhancement layer picturebeing smaller than the enhancement layer picture; determine the first ELportion of the enhancement layer picture that is to be predicted basedon the reference layer picture and a second EL portion of theenhancement layer picture that is outside the first EL portion from theenhancement layer offset values, wherein the first EL portion has ahorizontal picture size and a vertical picture size; upsample the RLportion, the upsampled RL portion having a horizontal upsampled picturesize equal to the horizontal picture size of the first EL portion and avertical upsampled picture size equal to the vertical picture size ofthe first EL portion; and encode or decode the first EL portion based onthe upsampled RL portion, wherein the processor is configured to alignthe upsampled RL portion with the first EL portion and predict samplesof the first EL portion from co-located samples of the upsampled RLportion, and encode or decode the second EL portion.
 2. The apparatus ofclaim 1, wherein the plurality of enhancement layer offset values arerepresented in units of luma samples.
 3. The apparatus of claim 1,wherein at least one of the horizontal upsampled picture size or thevertical upsampled picture size is smaller than a horizontal picturesize or a vertical picture size, respectively, of the enhancement layerpicture.
 4. The apparatus of claim 3, wherein the processor is furtherconfigured to determine a size difference between a size of theupsampled RL portion and a size of the enhancement layer picture andenlarge the upsampled RL portion based on the size difference.
 5. Theapparatus of claim 4, wherein the processor is further configured to:determine padded pixel values based on values of corresponding nearestboundary pixels in the upsampled RL portion, wherein to encode or decodethe second EL portion, the processor is configured to predict samples ofthe second EL portion from co-located padded pixel values of thedetermined padded pixel values.
 6. The apparatus of claim 1, wherein theprocessor is further configured to determine an upsampling ratio for oneor both of a horizontal direction or a vertical direction based at leastin part on one or both of a size of the first EL portion and a size ofthe RL portion.
 7. The apparatus of claim 1, wherein the apparatuscomprises a video encoder.
 8. The apparatus of claim 1, wherein theprocessor is further configured to generate an inter-layer referencepicture based on the upsampled RL portion.
 9. The apparatus of claim 1,the apparatus further comprising at least one of a digital television,digital direct broadcast system, wireless broadcast system, personaldigital assistant (PDA), laptop or desktop computer, digital camera,digital recording device, digital media player, video gaming device,video game console, cellular or satellite radio telephone, or videoteleconferencing device that comprises the memory and the processor. 10.A method of coding video data, the method comprising: encoding ordecoding a plurality of reference layer offset values each indicative ofa distance of a reference layer (RL) portion of a reference layerpicture in a reference layer from a corresponding edge of the referencelayer picture, the RL portion corresponding to a portion of thereference layer picture that is to be used to predict at least part ofan enhancement layer picture in an enhancement layer; determining the RLportion of the reference layer picture in the reference layer using theplurality of reference layer offset values, the RL portion being smallerthan the reference layer picture; encoding or decoding enhancement layeroffset values each indicative of a distance from corresponding edges ofthe enhancement layer picture to a first enhancement layer (EL) portionof the enhancement layer picture that is to be predicted based on thereference layer picture, the EL portion of the enhancement layer picturebeing smaller than the enhancement layer picture; determining the firstEL portion of the enhancement layer picture that is to be predictedbased on the reference layer picture and a second EL portion of theenhancement layer picture that is outside the first EL portion from theenhancement layer offset values, wherein the first EL portion has ahorizontal picture size and a vertical picture size; upsampling the RLportion, the upsampled RL portion having a horizontal upsampled picturesize equal to the horizontal picture size of the first EL portion and avertical upsampled picture size equal to the vertical picture size ofthe first EL portion; and encoding or decoding the first EL portionbased on the upsampled RL portion, comprising aligning the upsampled RLportion with the first EL portion and predicting samples of the first ELportion from co-located samples of the upsampled RL portion, andencoding or decoding the second EL portion.
 11. The method of claim 10,wherein the plurality of enhancement layer offset values are representedin units of luma samples.
 12. The method of claim 10, wherein at leastone of the horizontal upsampled picture size or the vertical upsampledpicture size is smaller than a horizontal picture size or a verticalpicture size, respectively, of the enhancement layer picture.
 13. Themethod of claim 12, further comprising determining a size differencebetween a size of the upsampled RL portion and a size of the enhancementlayer picture and enlarging the upsampled RL portion based on the sizedifference.
 14. The method of claim 13, further comprising: determiningpadded pixel values based on values of corresponding nearest boundarypixels in the upsampled RL portion, wherein encoding or decoding thesecond EL portion comprises predicting samples of the second EL portionfrom co-located padded pixel values of the determined padded pixelvalues.
 15. The method of claim 10, further comprising determining anupsampling ratio for one or both of a horizontal direction or a verticaldirection based at least in part on one or both of a size of the firstEL portion and a size of the RL portion.
 16. The method of claim 10,further comprising generating an inter-layer reference picture based onthe upsampled RL portion.
 17. An apparatus for processing videoinformation, the apparatus comprising: means for encoding or decoding aplurality of reference layer offset values each indicative of a distanceof a reference layer (RL) portion of a reference layer picture in areference layer from a corresponding edge of the reference layerpicture, the RL portion corresponding to a portion of the referencelayer picture that is to be used to predict at least part of anenhancement layer picture in an enhancement layer; means for determiningthe RL portion of the reference layer picture in the reference layerusing the plurality of reference layer offset values, the RL portionbeing smaller than the reference layer picture; means for encoding ordecoding enhancement layer offset values each indicative of a distancefrom corresponding edges of the enhancement layer picture to a firstenhancement layer (EL) portion of the enhancement layer picture that isto be predicted based on the reference layer picture, the EL portion ofthe enhancement layer picture being smaller than the enhancement layerpicture; means for determining the first EL portion of the enhancementlayer picture that is to be predicted based on the reference layerpicture and a second EL portion of the enhancement layer picture that isoutside the first EL portion from the enhancement layer offset values,wherein the first EL portion has a horizontal picture size and avertical picture size; means for upsampling the RL portion, theupsampled RL portion having a horizontal upsampled picture size equal tothe horizontal picture size of the first EL portion and a verticalupsampled picture size equal to the vertical picture size of the firstEL portion; and means for encoding or decoding the first EL portionbased on the upsampled RL portion, comprising means for aligning theupsampled RL portion with the first EL portion and means for predictingsamples of the first EL portion from co-located samples of the upsampledRL portion, and means for encoding or decoding the second EL portion.18. The apparatus of claim 17, wherein the plurality of enhancementlayer offset values are represented in units of luma.
 19. The apparatusof claim 17, further comprising means for determining a size differencebetween a size of the upsampled RL portion and a size of the enhancementlayer picture and enlarging the upsampled RL portion based on the sizedifference.
 20. A non-transitory computer-readable medium having storedthereon instructions that, when executed by a processor, cause theprocessor to: encode or decode a plurality of reference layer offsetvalues each indicative of a distance of a reference layer (RL) portionof a reference layer picture in a reference layer from a correspondingedge of the reference layer picture, the RL portion corresponding to aportion of the reference layer picture that is to be used to predict atleast part of an enhancement layer picture in an enhancement layer;determine the RL portion of the reference layer picture in the referencelayer using the plurality of reference layer offset values, the RLportion being smaller than the reference layer picture; encode or decodeenhancement layer offset values each indicative of a distance fromcorresponding edges of the enhancement layer picture to a firstenhancement layer (EL) portion of the enhancement layer picture that isto be predicted based on the reference layer picture; determine thefirst EL portion of the enhancement layer picture that is to bepredicted based on the reference layer picture and a second EL portionof the enhancement layer picture that is outside the first EL portionfrom the enhancement layer offset values, wherein the first EL portionhas a horizontal picture size and a vertical picture size; upsample theRL portion, the upsampled RL portion having a horizontal upsampledpicture size equal to the horizontal picture size of the first ELportion and a vertical upsampled picture size equal to the verticalpicture size of the first EL portion; and encode or decode the first ELportion based on the upsampled RL portion, comprising instructions thatcause the processor to align the upsampled RL portion with the first ELportion and predict samples of the first EL portion from co-locatedsamples of the upsampled RL portion, and encode or decode the second ELportion.
 21. The non-transitory computer-readable medium of claim 20,wherein the plurality of enhancement layer offset values are representedin units of luma samples.
 22. The non-transitory computer-readablemedium of claim 20, wherein the instructions further cause the processorto determine a size difference between a size of the upsampled RLportion and a size of the enhancement layer picture and enlarge theupsampled RL portion based on the size difference.
 23. The apparatus ofclaim 1, wherein the processor is further configured to, in addition toencoding or decoding the plurality of enhancement layer offset valuescorresponding to the plurality of reference layer offset values, encodeor decode one or more additional sets of enhancement layer offset valuesthat each correspond to a different portion of the enhancement layerpicture.
 24. The method of claim 10, further comprising, in addition toencoding or decoding the plurality of enhancement layer offset valuescorresponding to the plurality of reference layer offset values,encoding or decoding one or more additional sets of enhancement layeroffset values that each correspond to a different portion of theenhancement layer picture.
 25. The apparatus of claim 23, wherein theprocessor is further configured to, in addition to encoding or decodingthe plurality of reference layer offset values corresponding to theplurality of enhancement layer offset values, encode or decode one ormore additional sets of reference layer offset values that eachcorrespond to a different one of a plurality of reference layers used topredict the enhancement layer picture.
 26. The method of claim 24,further comprising, in addition to encoding or decoding the plurality ofreference layer offset values corresponding to the plurality ofenhancement layer offset values, encoding or decoding one or moreadditional sets of reference layer offset values that each correspond toa different one of a plurality of reference layers used to predict theenhancement layer picture.